Bonding process



Aug. 9, 1966 B. CHUDZIK 3,264,731

BONDING PROCESS Filed March 11, 1963 2 Sheets-Sheet 1 INVENTOR BRUNO CHUDZIK United States Patent 3,264,731 BONDING PROCESS Bruno Chudzik, Wenonah, NJ., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., 21 corporation of Delaware Filed Mar. 11, 1963, Ser. No. 264,373 15 Claims. (Cl. 29-486) This application is a continuation-in-part of copending Application Serial No. 118,376 filed June 20, 1961 in the name of Bruno Chudzik.

This invention relates to a method of bondingmetals. More particularly, this invention relates to a method of bonding metals by explosive means.

In accordance with the present invention there is provided a method for forming a substantially continuous metallurgical bond between metal layers which comprises forming a juncture between at least two metal layers, said juncture being defined by an angle of at least about 1, positioning a layer of a detonating explosive on the external surface of at least one of the metal layers, and initiating the explosive so that at least one of the ratios of the collision velocities to the respective sonic velocities of the metal layers is less than 1.2 and when each of these ratios is greater than 1.0 the angle between each two adjacent metal layers in the collision region exceeds the maximum value of the sum of the deflections produced in the metal layers by oblique shockwaves.

The term metal layer as used herein refers to a layer of a single metal or of an alloy of two or more individual metals or to a plurality of single layers bonded together.

The term juncture as used herein refers to the arrangement of one metal layer with respect to the other metal layer such that the two layers meet or substantially meet at a single point or along a single line. In either case, the planes in which the internal surfaces (i.e., the surfaces to be bonded) of the two metal layers lie, intersect along a given line, i.e., the two layers are not parallel. Hereinafter, the planes in which the internal surfaces of the metal layers lie are designated simply as the planes of the two metal layers.

The expression said juncture being defined by an angle of at least about 1 as used herein means that an angle, 6, between the two metal layers measured in any plane perpendicular to the line of intersection of the planes of the two metal layers is at least about 1.

The term external surface of a metal layer as used herein refers to that surface of the metal layer parallel to the inner surface to be bonded of the metal layer.

Reference is now made to the attached drawings for a more complete understanding of the invention. In the drawings like numbers indicate similar elements and FIGURE 1 is a cross-sectional view of an assembly which may be used to practice the invention in which a layer of a detonating explosive is positioned on the external surface of one of the metal layers;

FIGURE 2 is a cross-sectional view of another assembly which may be used to practice the invention in which a layer of a detonating explosive is positioned on the external surface of each of the metal layers;

FIGURE 3 is a cross-sectional View of a bonding assembly during the course of detonation of explosive layers positioned on the external surfaces of each of the metal layers;

FIGURES 4A to 4B are top views of bonding assemblies in each of which an explosive layer is to be initiated at a single point or along a single line on the explosive layer;

FIGURE 5 is a cross-sectional diagram illustrating the r 3,264,731 Patented August 9, 1966 "ice geometry and dynamics of a bonding assembly having an explosive layer on one metal plate; and

FIGURE 6 is a cross-sectional diagram illustrating the geometry and dynamics of a bonding assembly having an explosive layer on both metal plates.

In FIGURE 1, metal layer 1 forms a juncture with metal layer 2 which rests on a supporting means 3, e.g., of metal, wood, or gypsum cement, the angle between metal layers 1 and 2 being maintained by means of a spacer bar 4. A layer of a detonating explosive 5 to which is attached an initiator 6 having lead wires 7 to a source of electric current is positioned on the external surface of metal layer 1.

In FIGURE 2, metal layers 1 and 2 rest on supporting means 3. A layer of a detonating explosive 5 to which is attached an explosive cord 8 is positioned on the external surface of each of the metal layers and the explosive. cordss are attached to an initiator 6 having lead wires 7 to a source of electric current.

Although it is not intended that the invention be limited by any theory of operation a discussion of the mechanism by which bonding is achieved elucidates the extent to which process conditions can be varied or modified within the sense and scope of the invention and facilitates selection of optimum conditions for bonding in a given system. It is believed that the formation of a continuous metallurgical bond between the adjacent surfaces of two metal layers or plates is dependent upon a jetting phenomenon which occurs as illustrated schematically in FIG- URE 3. When the layer(s) of explosive 5 is initiated (9 representing the gaseous detonation products) the pressure produced by the detonation propels the metal plate(s) upon which the explosive rests toward the adjacent metal plate. When the metal plates collide at an appropriate angle and the collision region progresses across the metal plates at an appropriate velocity the pressure produced by the collision is transmitted slightly ahead of the collision region and forces the surface layers of the opposing metal plates to be thrown forward at high velocity from the collision region, i.e., to form .a jet 10. The removal of the surface oxides and other contaminants by the jet allows the underlying clean metal of the two opposing plates to be brought into intimate contact thus forming a continuous metallurgical bond 11 at the common interface between the two plates. In some instances, the jet escapes completely from between the two plates removing the surface oxides and other surface contaminants from the bonded system. In other instances, the jetted material is trapped between the two plates. In the latter cases the high kinetic energy of the jet causes melting of the adjacent clean surfaces of the metal plates and the melted material rapidly solidifies providing a bonding zone characterized by the presence of a homogeneous mixture of the metals of the two opposing plates which bonding zone contains the surface contaminants in a dispersed state so that they do not hinder bonding. The bonding zone can comprise a uniform layer of the homogeneous mixture of the metals of the two opposing plates or, if the trapped jet oscillates as it moves ahead of the collision region, the bonding zone may contain only discrete pockets of the mixture at more or less periodic intervals across the interface between the plates. In any event, a sound, substantially continuous metallurgical bond is produced.

Since the appropriate collision :angle and velocity required for jetting vary from system to system it is necessary to explain, first, how this angle and velocity can be determined for a given system, and, second, how the process conditions can be adjusted to insure collision and velocity.

In the following discussion 1 :and 2 refer to the? two colliding metal plates. V and V denote the velocities of the collision region relative to plates 1 and 2, respectively, or the velocities with which the two plates move into the collision region; C and C represent the ;bulk sound. velocities of plates 1 and 2, respectively, .bulk sound velocity being defined as the velocity of a plastic shock'wave whichforms when an applied stress just exceedsthe elastic limit for unidimensional compression:

of theparticular metal or metallic system involved; V is the relative plate velocity or the velocity with'which the plates approach oneanother and 1/ is the angle between; It is assumedthat the values of V V and p which describe the collision:

plates 1 and 2 in the collision region.

are changing slowly enough as the collision proceeds that the flow'of metal inthe collision region'at any: instant.

may-be describe-d approximately as a locallysteadyfidw.

When either V is lessthan C and/ or V is less than.

C bonding is achieved as long as V exceeds'a minimum value [required to produce sufiicient pressure in the, colli-j' sion region to overcome the elastic strength or exceed the V ela'sticlir'nit of atleastone of the metal plates andgthus provide the plastic deformation required for jetting. The minimum relative plate velocity for any particular metal system depends on the propertiesof the metal plates and f increases with increasing strength, hardness, and surface roughness. This minimum; value ofV necessary; for bonding stainless steel to carbon steel,'for example, is

about 90 meters per second if the surfaces of the metal platesa-re fairly smooth.

When both-V exceeds C and Vb eXceeds 'C collision results in the formation of oblique shock waves'in;

If these shock waves are attached to thecollision line, the pressureyproduced by the collisioncannot be transmitted ahead of the shock waves, i.e., cannotn bothplates.

be transmitted ahead of the collision region, and, there- Values ofp andKtor andw are readily ,availablef in Thevalue of the sonic'velocity, .C; of a metal or metal. lic .system may .beobtained by means of the-relation 1 where K is the..adiabatic bulk modulus indynes/em and i p is thedensity ingram's/cmi" ValuesofKtmay be ob-v and Poissons tainedfrom values of, Youngsmodulus, E, ratio, 1/, by meansof the relation the literature (see, for: example, American 'lnstitute of Physics. vHandbook, McGraw-Hilhf New York, 1957-). 7 Alternatively, the sonic1;velocity'may be. ascertained, from-published'values of the velocity of'th e plastic shock wave. as a function of the :particle velocity imparted to.

the metal by the shock wave in the manner; describedby R. G.. McQueen and 'S." P; Marsh, Journal of Applied Physics 31, 7 1253 (19,60):

' where-C is theavelocity of elastic compressional waves fore, a jet cannot be formed. Instead, the oblique' attached shock waves sharply deflect the metal plates, leaving the=surface contaminants at the interface and thus preventing bonding. The shock waves are reflected fromz the external free surfaces of the colliding plates'as rarefaction waves which either cause the plates tosepar'ate, at high velocity or produce spalling in one ofthe plates: If,.however, V exceeds a minimum value required to.

make'the collision angle ip exceed a criticallvalue, c

the oblique shock waves becomedetached from the col-3.

lisiontregion and stand ahead of the collisionline. In

this situation pressure is transmitted ahead of the collision region causing jet formation and making bonding possible}. The value of this critical angle difiers from systemto system and is dependent upon Va and Veg, and upon the material properties of metal plates 1 and 2...

When. both'V exceeds.1.2 C and V -exceeds '11 .C

good bonding is not obtained even when jetting occurs. Under these conditions an extremely high relative plate velocity, V is required in order to satisfy the condition for jetting, i.e., to make 1/1 exceed Q The excessive explosivelload needed'to produce this high plate velocity often causes gross deformation of the bonding assembly; Furthermore, the strong detached shock Waves which arereflected from the external free surfaces of the colliding plates as rarefaction Waves cause disruption of any tran-a e the thickness :of s the plate :andvelocitiesihigh. enough ,to.

satisfy .the :conditions. for: bonding are attained in dissient bond that is formed and contributeto the severe deformation and fracturing of the plates.

From the precedingvdiscussion it is obviousathat the.

values which must be determined before process conditions can be adjusted to insure jetting and, therefore,

bonding, are the sonic velocities of metal plates, 1 and 2,!

thevelocities withwhichthe plates move into thescolli sion region, and the relative plate velocity. In addition;

if thevelocities with which the plates move into the collisionregion exceed the respective sonic velocities-of. the

plates, the angle at which plates 1 and 2 collide andpthe.

critical collision angle which must be exceeded in orde to insure jetting must be determined.

described by R. G. McQueen and SP. Marsh (loc. cit.) and in :references cited by them.,. Alternatively. Clmay. be ascertained from the relation 3 (3): e eva e o r i 7' and C is the velocity ofrelastic shear waves in the metal.

' The required velocities of the elastic shear waves may be 2 For illustrative. pur-r i poses, .sonic velocity values for representative metalsrare a measured by well 'known vmethods.

given in thefollowing table.

Themethods 'for de term-iningycir Vzi V ,Irand \l/ are 1 mostieasily'unders-tood in the light of a discussion of the dynamics and geometry of 'a few'modifications of the novelprocess for explosively bonding metal layers-p Consider, for example, assemblies; in :which metal layi e-rs 1 and 2 areypositioned so! that. a juncturefin thesense defined above iislj-forrned .between; the two plates, and a layerqof explosive 'is positionedfion the external. surface oione or both plates; When the'explosive layer, or I layers are initiated the'. pressures produced by the detonations rapidlyiaccelerate: thead-jacentmetal plate.

or plate-s tohi-gh velocities; 'Usua-l-ly the maximum velocity fora given plate? is reached;in a distance equal .to

tances equal v to only .fractions' of theithicknessof the plate. 1 If each explosive layer is uniform in" thickness and other physicalproperties and if each layer isinitiated simultaneously over its'entirefsurface, e.g.,-using a plane wave generator, thenadjacent'metalsplaite moves "ina direction *essentially. perpendicular toit's original plane position and collides withjthe other metahplate at a n angle, 1,b, which is equal -to :the originaltangle, 6, between theplates. I

In the first ,case inwhicha layer of explosive positioned on. the externalsurface of, for example, metal plate v1,

is initiated simultaneously. overrits entire surface, metal plate 1 moves atfla velocity, V which is, equal to the relative plate velocity, V and collides, with metal plate 2. In this first case ;V ;andi 1V are determined solely by the initial angle, 6, between .the metalplatesiand'the Ifiliterature data are unavailablei'values of Cmay'be obtained by carrying out 'shock wave measurements. as

relative plate velocity, V and may be calculated by means of the relations In the second case in which layers of explosive positioned on the external surfaces of metal plates 1 and 2 are both initiated simultaneously over their entire surfaces, metal plate 1 moves at a velocity, V and metal plate 2 moves at a velocity, V The relative plate velocity, V is equal to the vector sum of V and V and may be calculated by means of the relation The metal plates collide along a plane which makes angles of 6 and 6 with the original planes of metal plates 1 and 2, respectively. These angles, like the original angle, 6, between the metal plates, are measured in any plane perpendicular to the line of intersection between the original planes of the metal plates and may be calculated by means of the relations (7) cos 6I V +VP1 and cos 5Z VP +V COS 5 In this second case V and V are determined solely by the initial angle, 6, between the metal plates, the plate velocities, V and V and the relative plate velocity, V and may be calculated by means of the relations V -VP, cot anticos and VP2 V1 1+V cos 5 Vcz- 62VP2 cot anticos In either the first or the second case the angle, 6 or it, is, of course, known and the plate velocities, V and V may be determined experimentally by any of several methods well known to the art. One such method for determining the velocity of an explosively propelled metal plate involves the use of electrical contact pins and is described by D. Ban-croft, et al., Journal of Applied Physics 27, (3), 291 (1956). An optical method is described by W. A. Allen, ibid. 24 (9), 1180 (1953), and a method involving use of flash X-r-adiographs is described by A. S. Balchan, ibid. 34, (2), 241 (1963).

In the first case V and V can be calculated directly from the experimentally measured V (=V In the second case V must first be calculated from the experimentally measured V and Vpz by means of relation (6).

If V and/or V are smaller than the respective sonic velocities of metal plates 1 and 2 in order to insure bonding it is merely necessary to determine the minimum relative plate velocity, V necessary to overcome the elastic strength of at least one of the metal plates. Since the relative plate velocity increases with increasing loading of a given explosive and with decreasing thickness and density of the explosively propelled metal plate(s) this minimum relative plate velocity can be determined experimentally by adjusting the explosive loading and plate thickness and density until some value of V at which jetting consistently occurs without accompanying gross deformation of the metal plates is found.

If, however, V and V exceed the respective sonic velocities of the metal plates, oblique shock waves are formed in. the plates and I must be determined before process conditions can be controlled so that it exceeds d thus meeting the condition necessary to insure detachment of the shock waves from the collision line and permit jetting.

When the oblique shock waves are attached to the collision line they sharply deflect the metal plates by the angles and e respectively, and the angle between the plates in the collision region, x/ is equal to the sum of these deflections which sum is designated as I (i.e., I The value of D for a given system is dependent upon V and V and upon the material properties of the metal plates and it is the maximum value of I for the given system which is equal to h and which t must exceed to permit jetting.

The deflection angles and may be calculated from the properties of oblique shock waves in metal plates by means of the relations tan 5 VC12 UM Us and UM(VC2 s tan z 02 M s in which U is the velocity of the shock wave measured normal to the shock front and U is the change in the velocity of the material caused by the shock wave.

The velocities, U and U are related to the pressures and densities ahead of and behind the shock fronts in the metal plates by the mechanical shock equations Po s=P( s- UM) and ( P P0=P0USUM in which p and P and p and P are the densities and pressures ahead of and behind the shock fronts in the metal plates. The density ahead of the shock front, p' is simply the known density of the metal plate at ambient pressure and temperature and the pressure ahead of the shock front, P is simply ambient pressure. Since the ambient pressure is generally around 1 atmosphere it is negligible compared to the pressure behind the shock front, P, and the second relation (14) becomes =Po s M A considerable body of published data is available, usually in the form of Hugoniot curves, which give the relationship betwen P and V(=l/ p) behind shock fronts in many metals. Thus by substituting a number of values of P and V(-=l/ in the mechanical shock equations a number of values of U and U for each of the metal plates are obtained. Alternatively U and U may be measured experimentally as described by Walsh, I. M., Rice, M. H., McQueen, R. G., and Yarger, F. L., Physical Review 108, (2), 196 (1957), and the corresponding values of P and p, calculate-d using the mechanical shock equations.

The values of U and U and the values of V and V are substituted in the equations for tan and tan M, respectively, and a number of values of and are obtained. The values of p and at each of a number of given pressures are added together to give a number of values of I Finally, the values Olf Q are plotted against the corresponding pressures and the resulting curve goes through a maximum. It is this maximum value of d which is equal to 4 and which ,0 must exceed in order to insure detachment of the shock waves from the collision line and thus to insure jetting. Since ,0 is equal to 6, it can be changed by changing the initial angle between the metal plates.

If an explosive layer is initiated at a single point or along a line, instead of with a plane wave generator, detonation progresses across the explosive layer at the detonation velocity, D, of the explosive in a direction essentially parallel to the original plane position of the adjacent metal plate 1 or 2. Thus the pressure produced by the detonation acts progressively on the adjacent metal plate 1 or Z to propel it toward the other metal plate, i.e., the pressure acts first on those portions of the adjacent plate which are closest to the point or line of mi,-

tiation; Under these conditions adjacent metal plate '1 or 2 'is deflected by an'angle 7 or y and travels at a velocity V or V in a direction which forms an angle of with'the perpendicular to the original plane position of the plate.

The angle, 5, as defined above is an angle between metal plates 1 and" 2 in any plane perpendicular to the line of intersection of the planes of the two plates This angle simply'defines theinitial arrangement-of the,

platesand is independent of the method of initiation and the consequent pattern of propagation of detonation ;of an explosive layer placed on the external surface of metal plate 1 or 2. There is however an angle, x,.which tor agiven arrangement 'of the plates at an initial angle,

fijcan vary in a manner dependent-upon the direction in t which detonation progresses across an explosive layer; Properly'speaking, there are two such angles: x which'is the angle between the initial line of intersectionof the planes of the metal plates and any line on metal plate 1' along which detonation is propagating and A which is the angle between the initial line of intersection of the 7 planes of the metal platesv and any line on metaltplate 2;

along'which'detonation is propagating. However, for

practical reasons which are discussed in greater detail. hereinafter, when explosive layers are positioned. on the the external surfaces of both metal plate 1 and metal plate 2, both layers have substantially the same detonation velocity and are initiated in substantially the same layers: placed on metal plates 1 and 2 are substantially the same and j =)\g= The directionof the initial line of intersection between detonation is proceeding away from the lineof intersection the angle, x, is generated by rotating the line of inter.-

section counterclockwise-until is coincides with the; line of detonation and 7t 'is positive and between 0 and 1P0! 0 and 180*. Conversely, vwhen detonation is proceeding toward the line ofrintersection, the angle, A, is generated by rotating the 'line of intersection clockwise until it coincides with the line of detonation; x is negative and Obviously, when between 0 and -1r or 0 and l80. detonation is proceedingparallel to the line of inter,-

section there is no angle betwenthe two lines,-i.e., \=0' or 12'. FIGURES 4A to 4B illustrate the values of k at various locations on the surface of the bonding assembly Whenthe explosive layer 5 is initiated at a point,-e.g., by means of an initiator 6 having lead wires 7 to a source of electric current or along a line, e.g., by means of aline wave generator 12. 'Ineach of these drawings the line AB approximates the line of intersection of ;the planes of the metal plates, the solid lines marked with arrows indicate the directions or the lines along which detonation propagates when the'explosive layer is ini-.

tiated as shown in the drawing, and the broken :linesare extrapolations of the lines along which detonation propagates. The geometrical relationships among Vc1, V D, V 6, 1p, and v when an explosive layer positioned on the external surface of metalplate 1 is initiated so that;

A=90 are illustrated'in FIGURE 5. The geometrical relationships among V VC D, V V V 6,6

6 1,0, n and 'y when' explosive layers positioned on the 7 external surfaces of metal plates 1 and 2 are initiated simultaneously so that A=90 are' illustrated inFIG-i URE 6.

When the explosive layer-(s) is initiated at a point or manner, i.e., the patterns of propagation of explosive the planes of the metaliplatesis defined so that when? 7 section-overrthe entiresurfaoe of the layer, i.e., x=90 (see FIGURE'4A) andthe equations forV and V g i along a line it is necessary, just as it is necessary when a plane wave generator is used, to determine the values:

of "V and V for a given system.x However, whena 7 single. explosive layer'positioned on the vexternal surface of, for example, metal plate :1 ;isinitiated at a point or r along a line,:.Y and V depend on 6,1 A, and D and when explosive layersipositionedl on the external surfaces of'bothm'etal platesrarewinitiated:simultaneously at 211 point oralong'a line oneach-layer, ,V d pends 011551, t

A, andD andV depends? ont fi 7 x, and D.

velocity,;Y by means of the relation The collision velocities of plates 1 {and 2 areobtained, by substituting the valuesfof 6, A; v and, D, determined a as indicated in the preceding paragraph; in the following equationsand solving the equations vfoi Vm-and V Sinantitan [1 tan tan 5 S111 A] em 114 S111)? cos x cos A sin 71+c'os'7 tan5 sin 2w- [l tan tan 5 sift] gin" 71 00s? A a sin antitan 'sin A cossh cos A: cos 5-[l |eot 'y tan 6 sin cos These'equations are [simplified when-as iss'ofiten econ venient, i'the, :explosivexlayer llS 1 initiated simultaneously along' an entire edge: of the layer, e.g.,- byjneans of. a linerwave generatorattached to one edge of the layer. Whenthis edge is parallel :to or coextensive'withlthe line of intersection of the planes of the metalgplatesdetonae 7 tion proceedsin a directionmormalqto the llfleibf interare reduced to the ,-following forms..

' sinz'y COS D Sm'hlrka) coal 2 (20.) V Veg; sin

or +5) V When this edge is perpendicular to-the'lin'e of intersec-t tion detonation proceeds in"a.;direction parallel to the line of intersection'over the entire'surfacefof the layer, i.e., x=0 or (see FIGUREAB) and theequations are reducedto the following ftorms.., 1

Considering the ,SQCOl'ldICfEtS; i.e., an explosive layer positioned on the'sexternal surfaces'of-both metal plates, Dtis known; the angles, 'y -,and can'bedetermined as indicated in thetprecedingi paragraph; and the angles;

6 and 8 are the solutions of-the two equations 11 sin antitan (1 tan 2 tan 8 s1n A s1n 'y s1n A cos A cos A sin v +cos y; tan 6 sin A (1-tan 71/2 tan sin A) sin 7 cos A and Y2 sin antitan| tan 2 cos A sin 'Y2'i'COS 72 tan 6 sin A tan 6 sin A) sin y; sin A cos A (1-tan tan 5;, sin A sin 72 cos A Having determined V and V either the first or second case if V and/or V are smaller than the respective sonic velocities of metal plates 1 and 2 bonding is achieved as long as V exceeds a minimum value necessary to overcome the elastic strength of at least one of the plate.v In the first case V =V and the minimum value of V may be determined and V changed as described above with reference to plane wave initiation of a single explosive layer positioned on the external surface of metal plate 1. In the second case V is a tune-- tion of Vpl and Vpg which may be calculated by means of the relation The minimum values of Vp and V required to give a value of V which exceeds a minimum value necessary to overcome the elastic limit of at lea-st one of the plates may be determined and V and V92 may be changed as described above with reference to plane wave initiation of a single explosive layer. If, in either the first or second case, V and Veg exceed respective sonic velocities of metal plates 1 and 2, I must be determined as described above and 1/1, adjusted so that it exceeds the calculated value of While \I/ is equal to 6 when plane wave initiation of the explosive layer is employed, when the explosive is initiated at a point or along a line the collision angle ,0 may be determined by means of the relation Cl C2 P and may be increased by increasing V by adjusting process conditions as described above.

The process of the invention is applicable to bonding a wide variety of metals, such as steel, copper, aluminum, iron, titanium, niobium, chromium, cobalt, nickel, beryl- -lium, magnesium, molybdenum, tungsten, copper, gold, and their alloys, and other metals, many of which are very difficult to bond by any of the conventional techniques. As stated previously, each of the metal layers may be a single metal, an alloy of two or more individual metals, or a composite of two or more single layers. The only limitation on the physical properties of the metal layers is that they be ductile, i.e., that they withstand permanent deformation without fracturing under an explosive load. The surfaces of the metal layers do not require any preparation to remove surface impurities prior to being subjected to the bonding procedure. How- 10 ever, if desired, the surfaces may be subjected to a degreasing and/or a mild abrasive treatment.

The metal layers can be of any desired dimensions and need not be fiat plates of uniform thickness. For example, either or both of the layers can be wedge-shaped, i.e., of graduated thickness, curved, dished, or bent at some angle. Moreover, more than 2 metal layers can be bonded together in a single operation, for example by providing an interleaf between two outer layers to be bonded. One or more of the metal layers may be a portion Of the surface of a unit of equipment to which a coating layer is to be affixed.

Many arrangements of the metal layers to be bonded may be used in the practice of the present invention. The metal layers may actually meet to form a juncture along a line or at some point such as a corner on the internal surface of each of the layers. Alternatively the metal layers may be spaced a small distance from one another at the point or line on each of the layers which is closest to the line of intersection of the planes of the layers. However, since jetting does not occur unless the layers achieve some minimum velocity, V relative to one another before colliding, when the former arrangement is used a small region adjacent to the line or point of contact between the metal layers remains unbonded in an otherwise continuously metallurgically bonded system.

The angle, 8, which defines the juncture between the metal layers to be bonded need not be constant over the entire area of each of the layers. For example, when the intern-a1 surface of one or both of the metal layers is curved or dished, 6 is the angle between the plane tangent to the internal surface of the layer at a given point on the layer and the plane of the internal surface of the metal layer to which it is to be bonded, 6 being measured in any plane perpendicular to the line of intersection of these two planes. When more than 2 metal layers are to be bonded together in a single operation the angle, 6, between any two adjacent layers may be the same as or different from the angle, 6, between any other two adjacent layers.

The method employed to maintain the angle, 5, between the metal layers prior to initiation of the explosive is not critical. The angle may be formed, for example, by resting one edge of a first metal layer against a corresponding edge of .a second metal layer so that the metal layers are in a standing position on any supporting surface as shown in FIGURE 2. Alteratively, a supporting means, e.g., spacer bars or struts as shown in FIG- URE 1, may be used to maintain 6 providing that the supporting means do not interfere with the bonding procedure, i.e., by shielding large areas of the surface to be bonded or retarding the acceleration of the metal layer(s) upon initiation of the explosive layer(s). In cases where the metal layers to be bonded comprise overlapping ends of the same or of two different metal sheets, e.g., in seaming pipes or plates, 5 may be provided by bending one overlapping end away from the opposing overlapping end. Rigid supporting means for the entire assembly to be bonded such as are shown as 3 in FIGURES 1 and 2 are not necessary and the entire assembly may, for example, be immersed in water.

The composition of the explosive layer(s) is not critical. For example, a layer of any cast, granular, gelatinous, flexible 0r fibrous explosive composition based on pentaerythritol tetranitrate, cyclotrimethylenetrinitramine, trinitrotoluene, or ammonium nitrate, or mixtures thereof with each other with other explosive or nonexplosive components may be used in the process of the present invention.

An explosive layer may be positioned on the external surface of one or both metal layers and may be held in position by any suitable means such as tape, glue, etc. Obviously when more than two metal layers are bonded together in a single operation to form a single bonded composite the explosive layer is placed only on the ex.- I

ternal surface. of one or both of the outer metal layers.

Alternatively, an assembly of metal layersto be bonded may be placed 'on each 'of the two opposite surfaces of a single explosive layer, thus permitting two bonded composites to be formed simultaneously. In'this latter. case when a single layer of explosive is used,.the collisionhof x the outer metal layer upon :which the explosive is placed with aninterleaf metal layer is considered to be .a -col lision between a moving metal layer and a substantially stationary metal layer and the collision of the composite" comprising this first metal layer and the interleaf withother; outer metal layer is considered. to be a second collision of substantially the same type. When two layers of explosive are used,1the collisions of both outermetal layers with the respective adjacent surfaces of an interleaf metallayer are consideredto be collisions between a moving. metal layer and a substantially stationary metal layer. 7 1

One' limitation which must be made on the initial angle which defines the juncture between the metal layers and on the loading, detonation velocity, and method of initia-.

tion of the explosive layer.(s) used is that they'be adjusted sothat the two critical requirements for bonding be met.-

As. is apparent from the preceding discussion of. the

mechanism by which bonding occurs; one critical require- 7 ment:fr bonding is that the ratio of the collision velocity to the sonic velocity of. at least one ofthe metal layers be less than 1.2, i.e.

Thesecond critical requirement for bonding, which must be considered only if the .ratios of the collision velocities of both metal layers to the respective sonic velocities of the layers are greater than 1 is-that the angle between the metal layers in the collision region exceed some critical.

value, i.e.

when

1 and 1 Since the sonic velocity of a given metal layermust'be considered to have a known fixed value it is the collision Velocity which must becontrolled by a suitable adjustment' of process conditions in order to meet :the .first critical requirement for bonding.

When a layer of explosive on the external surface of lates'tofthe'weight' distributionperunit area-ofthe ex-1 plosive layenortlayers. -However, a buffer layer of some, material such as a polyester foam 5 or :film, .Masonite,

oneor of both metal layers is initiated simultaneously over its entire surface the collision velocities of the metal a line the collision velocities of the metal layers are functions; of the initial angle, 6, between the metal layers,

the angle, .7 and/CD1 by which the metal layenis deflected by the detonation pressure, the angle, which depends upon the pattern of propagation of detonation and=the detonation velocity, D, of the explosive. Thus in addition to the initial angle and the explosive loading (to which .7 and W are directly proportional), the method or location of the point or line of initiation and the. detonation velocity of the. explosive must beadjusted so that the ratios V /C and/or'V /C are less than 1.2.

In order to meet the second criticalrequirement for the meta-l layers.

bonding .the anglebetween themetallayers in the col l-isionregion ;must be controlled by a suitableadjustment.

of process conditions. When the entireexplosive layer(s), is? initiated simultaneously the fangle, b, at which the metal layers collide :is' equal to the .initial angle, 6,.be-

tween the layers-and, obviously it is increased by a cor- However, when the explosive.

responding increase in z 6. layer is initiatediat a:point or along a line on the layer his a function of thefcollisionvelocities ofthe metal layers and .of the relative plate velocity and the effectof adjustment of process conditions on ,0 depends upionthe. 7 effects of these adjustments on ;V V 2, and V ;(see

relation (28));

Within the limitation thatthe initial angle between the metala layers, and the loading, detonationsvelocity, and method of initiation of the explosive-layer(s) satisfy the two critical requirements forbondin'g many variations'are possible. i

It has. been found that when. the initialnangle between .3

the metal layers is between about l"=' and 40. the process ofthe .present invention'can be .carried out .without ex- .tensive deformation of the. .bonded system. However,

when the initial angle is or more thebo-nded system often is severely deformed byythetforces produced by detonation of the explosive layer. or layers. This. deformation can :be attributed at least in part to the factthat when vrnetal' layers arearranged'ar large angles with respect to one nother those portions of each layer which are furthestfrom the. juncturebetween thev layers must travel-relatively large distance'sbefore-collidingwith cor-- responding portionssofltheother layer. Over suchrelativelylargedistances :airi. between the layers mayact as a cushion preventing stable acceleration of the'layer or layers .to, theflappropriate velocity: for stable collision resulting in jetting. The .l ayer or layers may flap, for

oscillate .enroute. to. the" collision region and :this -phe-. nomenon as wellas laggingedges caused by theboundary effects at free surfaces, i.e., edges Ofthe layer or layers, T

contribute to the gross deformation and! or poorbonding observed when the initial angle between'themetallayers is 60or-more- For the same reasons, although the metal layers. neednot actually meet but may ;be separated by a smalld'istance atthe :point or linesclosest to the line of intersection of their planes, ithis distance should be kept vto amminimumand generally a separation of more :than

about 1 inch is neither: necessary nor desirable; V

Theexpressionexplosiveloading asusedherein rewater, tape etc. can be interposedbetweenlan explosive layer and the adjacent metal. layer in order to prevent surface contamination or 'roughening of' the metal layer.

Since such a buffer. layeramay .tendto attenuate the pres-. sure producedby detonation of a given explosivezat a given weight distribution, use .of such abuffenlayer may effectively reduce the explosive loading... Conversely, in creasing confinement'of an explosive layer may effectively increase .the explosive loadings, One .explosiveloading often :iS satisfacto-ry for a number ofdifierent' bonding systems.

the initial angleybetweenthe metall'ayers is 5 and when the-angle is 32?. tribution, and loading of explosive suitable in. any case will be readily apparent to one-skilled in the' art, consid ering such factors as typeofexplosive, thickness of the metal layer, etc.- wln-any case as: explained .above,-the explosive loading must be sufficientito produce a collision pressure .whichexceeds the-,elasticdirnit'of at-least oneof 0bviously,; excessive explosive may a cause undesired deformationand-should be avoided.

The explosive used. must be'l'a detonating'explosive- V Generally, I the minimum detonation 'velocity ;of the. ex-,

As is" shown in the examples, the amount of explosiveused for bonding tw'o'stainless steel 'plates of identical sizeis approximately the same forthe case'when Theiparticular amountgor weight displosive composition is at least about 1200 meters per second since below this velocity detonation is often unstable and the effect of the composition on the metal workpiece is often unpredictable. Generally the maximum detonation velocity is no more than about 9000 meters per second since the shock waves associated with explosive compositions having extremely high detonation velocities often cause spelling of one or more of the metal layers. The practical maximum detonation velocity for a given system will be obvious to one skilled in the art considering such factors as strength of the metal layers, etc. However if more than one explosive layer is used in a single operation the two layers should have at least approximately the same detonation velocity. Otherwise, the detonation front of the layer having the higher velocity may reach a point adjacent to an undetonated portion of the other layer and dislodge the undetonated portion from position. This effect, as well as anomalous effects due to interfering shock waves, is detrimental to formation of a continuously bonded, substantially undeformed composite. Although in some cases, the deleterious effects of explosive layers having different detonation velocities can be overcome, e.g., by simultaneous plane wave initiation of both layers or some other specially designed method of initiation, such a situation introduces unnecessary complications and is generally to be avoided.

The explosive layers may be initiated by any conventional initiating device, e.g., blasting cap, exploding wires, detonating cord, line wave generator, plane wave generator or any suitable combination thereof. The locationof initiation on one or both layers may be at a point, e.g., at a point along an edge, a corner, or in the center of the layer, along a line such as an edge of the layer, or simultaneously over the entire surface of the layer. However, when more than one explosive layer is used, both layers generally should be initiated substantially simultaneously at substantially corresponding locations on the two layers so that the pattern of propagation of detonation of the two layers is essentially the same. Otherwise difiiculties comparable to those mentioned above with reference to use of 2 layers of explosive having different detonation velocities may be encountered.

The process of the invention is particularly suitable for seam welding of metal sheets to form large, flat, continuous surfaces or rectangular containers and for seam welding of pipes or tubes. In such operations where the length of the surfaces to be bonded is substantially greater than their width, the explosive layer(s) is conveniently initiated at a point on the layer so that A= over a substantial portion of the layer, i.e., detonation proceeds along the length of the layer parallel to the juncture between the metal layers. This technique forces the air out from between the layers and insures a sound bond over the length of the seam.

The process of the invention is also particularly suitable for bonding thick metal layers, i.e., /2 inch thick or thicker. By employing a relatively large initial angle, 5' between the layers and adjusting process conditions so that the jet escapes completely from between the layers a thin bond zone comprising essentially a direct metal-tometal bond rather than a thick layer of solidified melt which may contain solidification or other defects can be obtained. Also, when a metal layer of relatively high density is propelled against a stationary metal layer of relatively low density, by employing a relatively large initial angle, 6, and adjusting process conditions so that the jet oscillates, a sound bond is obtained.

The strength of the substantially continuous metallurgical bond formed by the process of the present invention generally is greater than that of the weaker of the metal layers in the composite. The ductility of the bonded composite generally is comparable to that of the unbonded metal layers and it may be improved by heat treatment. Thus, if desired the bonded metals may be 14 subjected to further metallurgical operations such as forming, drawing, extruding, rolling, etc.

The invention may be illustrated by the following. In each of the examples the character of the bond between the metal layers is'determined -by ultrasonic testing and by metallogr-aphic examination of photomicrographs of polished and etched portions of the cross-sections of the composites produced.

Example 1 This bonding technique involves a single moving disk being driven against a stationary disk. The explosive employed is a thin, uniform sheet of a flexible explosive composition comprising 35% pentaerythritoltetranitrate, 50% red lead, and, as a binder, 15% of a 50/50 mixture of butyl rubber and a thermoplastic terpene resin [mixture of polymers of ,B-pinene of formula (C H commercially available as Piccolyte S10 (manufactured by the Pennsylvania Industrial Chemical Corporation). This composition has a detonation velocity of about 5000 meters per second. Complete details of this composition and a suitable method for its manufacture are disclosed in U.S. Patent 3,093,521.

A type 321 stainless steel disk 5% inches in diameter x 0.050 inch thick is placed on a supporting flat metal plate. A copper disk having the same dimensions as the steel disk is positioned in such a manner as to form an angle of 730 between the inner surfaces of the plates, i.e., the surfaces facing one another when the plates rest against each other along a section of the perimeter. The angle is maintained by taping the contiguous edges of the disk and placing a spacer bar opposite the contiguous surfaces. The surfaces of the disks are not treated in any manner to remove surface impurities. A conforming layer, i.e., S /s-inch disk of the above-described explosive composition, is attached to the outer surface of the copper disk by tape. The weight distribution of the explosive layer is 2 grams per square inch. After initiation of the explosive layer by a No. 6 electric blasting cap at the point where the metal layers are in contact, it is found that substantially continuous metallurgical bonding over the entire area of the interface between the two disks is achieved.

The metal composite thus produced is successfully formed into a cuplike configuration without any apparent fracture or separation of the bond by positioning a layer of a detonating explosive on the metal composite and initiating the explosive to drive the composite against a cup-shaped steel mandrel.

The following example illustrates the seaming of a metal sheet to form a pipe.

Example 2 A 7-inch x -inch aluminum sheet is wrapped around a 2-inch-diameter steel mandrel so that there is a l /z-inch overlapping portion of aluminum sheet. A As-inch space remains at the edge of the overlapping portion; the overlapping portion is in contact with the edge of the layer adjacent the mandrel. Thus the angle varies slightly but, in general, lies between 10 and 30. The steel mandrel has a light coat of petrolatum to prevent the aluminum from bonding to the steel mandrel. A 7-inch X l /z-inch strip of explosive is placed along the edge of the entire length of the overlapping portion of the aluminum sheet. The explosive is a uniform sheet of an explosive composition comprising, by weight, 75% pentaerythritol tetranitrate, 7.5% paper pulp, and 17.5% of a low-temperature polymerized acrylonitrile-butadiene elastomer containing a high percentage (approximately 40%) of acrylonitrile and having a specific gravity of 1.00, and a Mooney viscosity of 70-95 (commercially available as Hycar 1041 and manufactured by the B. F. Goodrich Co.). The weight distribution of the composition is 2 grams per square inch. This explosive composition is described in proximately 7 with the firstsheet.

15 US. Patent 3,102,833. After initiation of the explosive layer by an electric blasting cap, positioned in the center of one of the lVz-inch edges of thelayer, a firmly seamed pipe results wherein the-seam comprises a substantially j continuous metallurgical bond over the entire area of the interface between the ovenlapped ends of-the aluminum sheet. 7 v V 'To illustrate sea-m welding of metal sheets to form flat. continuous surfaces, the'following examples are given.

Example '3 An'aluminum sheet, 6 inches'x 2% inches x big-inch, is placed on a steel support. A second 6 x,2% x -inch aluminum sheet having a 1-inch, slightly bent portion 7 along the edge adjacent the fold. The explosive employed; is a slightly modified version of that described in Example 1 and comprises a layer of a .fiexible explosive compost: tion comprising 20% very fine pentaerythritol tetranitrate, 70% redlead, and, as a binder, a mixture of'8%. of thev binder described in Example 1 and 2% of polybutene having ,an average molecular weight of approximately 840, a specific gravity of 0.90-0.87, and a viscosity index of 108 (commercially available, as Polybutene ,24, and J manufactured by Oronite Chemical Company). The

detonation velocity of the explosive com-position is 4000.

meters per second and'the weight distribution is 5 grams" per square inch, After initiation of the explosive layer by an electric blasting cap positioned in the center of the 6-inch edge of the explosive which. is adjacent to the bend I in the second aluminumsheet, a firmly bondedone-inch "seam comprising a substantially. continuous'metallurgical 1 bond over the entire area ofrthe interface between the over: lapped ends of the .two sheets, joins the two sheets: 7

7 Example 4 I The procedure of Example 3 is followed to seam two copper sheets, each '6 inches x 2 inches x A inch, except. thatthe 1 inch x 6 inch strip of explosive used is a layer of a flexible composition comprising 72% pentaerythritol 1 tetranitrate, 6.5% nitrocellulose, and 21 .5% rof tri(2-eth yl- 2 16b persecond, The explosive composition. is the subjectof US. Patent 2,992,087, The-weight distribution of the ex plosive composition is 1.5 grams per square inch. .Afteririitiationof theiexplosive layer by an electric blastingcap, the two sheets are found, to be firmly bonded by a one-inch seam comprising asubstantially continuous metallurgical bend over. the entire area of the interface between the overlapped ends ofthe two sheets;

Table I presents. variations applicable in', the angular bonding technique of the invention, e.g., angle: range, types of metal, weight; distribution of -explosives, etc..

The; explosive .used in :all'of the :examples given in Table. I, except iExamples. 10,11, 21, and22 Zis that' described in Example 1. In yExamples 10 vand =11, the" j explosive usedisa slightly modified version of that de- 7 scribed inExamplezl and comprises a =flexible'explosive composition comprising 20% very--fine;pentaerythritol tetranitrate, 70% red-lead, and 10% of thC;bllldl",dC-. scribed in Example :1. In'JExamplesZl and 122, the ex-.

. plosive used isthat described in Example 3. 1

The bonding assemblies aresimilar to, that shown in FIGURE 2 andin allfofthe'examples, except Examples 5,:15, 20, 21f,'a'and 22, the-explosive layers are initiatedv by ;a combination of aN'o'- 6 electricxblasting cap-and detonating' cordspositioned asshown in FIGURE 2., 111' Example 5, the explosive'layers are initiatedbytwo line f wave generators-(such as described :in' U.S.;Patent 2,943,

571, issued July: 5, 1960; one .ofwhieh is attached *to. thatsedgetof'each explosive Iayeradjacent to the-juncture: between the metal layers, which in turnare initiated simul taneouslyY by: an electric blasting cap.;1'In;Example's'-15 and120 theycombinatio'n of electriciblastin'g cap'-and=detonating cords. is used; However,- in these examples acord is attached to the. center of1eachiexpl0sive=layer rather than toan edge,of-the, layeras'shown in FIGURE 2.

In Examples 21 and 22 the ,explosivelayers are initiated by means of'astrip of theexplosive composition described 7 in Example ,4 which is positioned so that: it is;in contact with that edge: of each explosivelayer; adjacentito'the: juncture; between the metal layers. oventhe. entire length;

. of that edge. The strip is in turn initiated-by means of a line wave generator and an electric blasting cap as described in connection with Example 5;, '1 In all ofthe examplesthemetal layers are foundto be.

substantially continuously metallurgically bonded'over the entirearea of the interface between themetal layers after initiation .of theexplosive layers." When lthe shear strengths. are determined according to A.S.T.M. Method y y- 3p p y T isc m No. A263-44T, the shear strengthsiof the bonded assempositionhas a detonation velocity of about6,900 meters blies are found to be :much higher than the minimum TABLE I Metal Layer 1 Metal Layer 2 Angle 1 Explosive i between 7 metal I Treatment Treatment layers, Size of each Weight Example Type Size (in) of surface Type Size (in.) r of surface deg. layer (111.) dlSgll/lfiltml i gml 5 304 stainless 2% x 2% x 1-62 None 3o4tstziinless 2% x 2% x 42". V 5 2%x 2%."

steel. s as 2 x2 x &2 d0 2V1: 2 x}2 2%): 2% A 4 /4 p 1 23A";

do- 9 Cleaned with 12 emery cloth. d0 d0 2 Mild steel 9 $4 d0 6x 6 x 7 d0 1% (diam;) x M6". None do 1%(d1am.),x M6 27 16.; 32ltsteinless 5% (diaml) x 0.05 do 321tst2imless 5% (d1am.) x 0.05 14 s ee V 5 es p Titanium 2% x 2% x 0.025....'. -do '304tst2iinless 2% x 2% x %z 2% x 2% V s ee Copper ,5% (diam.) x 0.05-.- do 321tstaiuless 5% (ell-3111.) 0.05 v 14 5% diam s ee Titauium 5% (diam.) x 0.05--. Annealed. Aluminum-.- 5% (diam) x 0.10-- 14: 5% dia.m Mild steel 1% (diam.) x M6..- N0ne l\/I11d 513691;... 1% (dlann) x is 40. 1% diam" V Nickel--- 4 x 5 n do Copper 4x 5 x Ms 40: 4 x 5 4 x 5 x V1 do do 4 x 5 x $46 4 x 5.0,

HH UICXIDJN N w CDWNNQ: 06 03059993 (20,000 p.s.i.) prescribed by A.S.T.M. specifications for this type of bonded assembly. For instance, the shear strengths of the bonded assemblies produced in Examples 11 and 12 are 54,100 and 60,400 p.s.i., respectively. Bonded assemblies produced by common conventional means usually exhibit a strength of only from 30,000 to 35,000 psi.

Table II presents data relative to bonding more than 2 metal layers in a single operation.

In all of the examples given in Table II the bonding assemblies are arranged substantially as shown in FIG- URE 2. However, a third metal layer or interleaf is interposed between metal layers 1 and 2. The explosive used in each of the examples is that described in Example 1 and the explosive layers are initiated as shown in FIGURE 2 and as described above in connection with Examples 6-14 and 16-19. After initiation of the explosive layers each of the outer metal layers is found to be substantially continuously metallurgically bonded to the interleaf over the entire area of the interface between the layer and the interleaf.

separation between them is 0.05 inch. However this minimum separation is between one corner of the stainless steel plate and the corresponding adjacent corner of the mild steel plate, i.e., they substantially meet at a single point, rather than along adjacent edges of the plates over the entire lengths of those edges as in Example 30. The angle between the plates in any plane perpendicular to the line of intersection of the planes of the two plates is and the electric blasting cap is positioned at that corner of the explosive layer which is adjacent to the juncture between the plates.

The invention has been described fully in the foregoing and it is intended to be limited only by the following claims.

What is claimed is:

1. A method for forming a substantially continuous metallurgical bond between metal layers which comprises forming a juncture between at least two ductile metal layers, said juncture being defined by an angle of about 1 to 60, positioning a layer of a detonating explosive on the external surface of at least one of the metal layers,

TABLE II Metal Layer 1 Interleaf Metal Layer 2 Angle Angle Explosive between between metal metal Ex. layer 1 layer 2 Size of Weight Type Size (1.11.) Type Size (in.) Type Size (in.) and and each layer distriinterleaf interleaf (in.) button 23..- Titanium.-. 2 x 7 x 0.025. 304 stainless steel. 2 x 7 x 2 Titanium. 2 x 7 x .025 1 3 2 x 7 2 (10-- 2x7x0.025 dO 2x7x }2 d 2x7x .025 5 5 2x7 3 do 2x7x0. 5 2x7X%2 2x7x.025 7 7 x7 2 26. d0 2 X 2 2%x2%x H 2- 2% X 2% x 0.025. 8 10 2% x 2V 3 27--- Mild steel-.- 3-layer com- 5% (diam.) 5% (diam.) 730- 730- 2 posite Cu/mild x 005. x 0.05. (diam steel/Cu. 28.-- Copper 5% (diam) Mild steel 5% (diarn.) Copper 5% (diam.). 730 730'. 5% 2 x 0.05. x 0.062. x 0.05. (diam 29--. 304 stainless 3 x 3 x M Alloy: 72 3 x 3 x 0.004.- 304 stainless 3 x 3 x Ma 5 5 3 x 3 3 steel. silver/28 steel. copper.

Example 30 and initiating the explosive so that at least one of the A mild steel plate 6 inches wide, 9 inches long, and inch thick is placed on a plywood slab and a 304 stainless steel plate 6 inches wide, 9 inches long and /3 inch thick is supported above the mild steel plate by means of steel spacer bars spot welded to corresponding points on the adjacent edges of the two plates. The plates are positioned so that the minimum separation between them is 0.05 inch along the entire length of adjacent 64inch edges of the plates, i.e., they substantially meet along a line and the angle between the plates is 10. The external surface of the stainless steel plate is covered with a layer of polystyrene foam linch thick which in turn is covered with a layer of the explosive composition described in Example 4 having a weight distribution of 5 grams per square inch. The explosive is initiated by means of an electric blasting cap positioned in the center of the explosive layer and after detonation the plates are substantially continuously metallurgically bonded over the entire area of the interface between them.

Example 31 A substantially continuously metallurgically bonded system is prepared using the materials and technique described in Example 30. However in this example the layer of explosive is initiated by means of a plane wave generator as described in US. Patent 2,887,052 issued May 19, 1959.

Example 32 A substantially continuously metallurgically bonded system is prepared using the materials and a modification of the technique described in Example 30. In this example the plates are positioned so that the minimum ratios of the collision velocities to the respective sonic velocities of the metal layers is less than 1.2 and when each of these ratios is greater than 1.0 the angle between each two adjacent metal layers in the collision region exoeeds the maximum value of the sum of the deflections produced in the metal layers by oblique shock waves, the loading of said explosive being at least that which produces a collision pressure greater than 100% of the elastic limit of the metal having the lowest elastic limit in the system.

2. A method for forming a substantially continuous metallurgical bond between metal layers which comprises forming a juncture between two layers of diiferent ductile metals, said juncture being defined by an angle of about 1 to positioning a layer of a detonating explosive on the external surface of at least one of the metal layers and initiating the explosive so that at least one of the ratios of the collision velocities to the respective sonic velocities of the metal layers is less than 1.2 and, when each of these ratios is greater than 1.0, the angle between said metal layers in the collision region exceeds the maximum value of the sum of the deflections produced in the metal layers by oblique shock waves, the loading of said explosive being at least that which produces a collision pressure greater than 100% of the elastic limit of the metal having the lowest elastic limit in the system.

3. A method as in claim 2 wherein a layer of a detonating explosive is positioned on the external surface of one metal layer.

4. A method as in claim 2 wherein a layer of a detonating explosive is positioned on the external surface of each of two metal layers, each of the layers of explosive having substantially the same detonation velocity, and the layers of explosive being initiated substantially simultaneously and at substantially corresponding locations on each "of the layers of explosive.

5. A method as inclaim 2 wherein the explosive is initiated at a point on an edge adjacentto the juncture between the metal layers;

6. A method as in claim 2 wherein the explosive is'ini-i tiated simultaneously along an entire edge adjacent to the 9. A method as in claim 3 wherein the explosive .is

initiated simultaneously over the entire surface of said layer of a detonating explosive.

10. A method as in claim 4 wherein each of said layers of explosive is initiated simultaneously over its entire.

surface.

11. A method as in claim 2 wherein said metal layers are positioned so, that they substantiallyiimeet"along'an entire edge of each of thelayers and the explosive is ini-,

tiated along :an edge; of the bonding assembly. perpendic-N ularto said first edge:

12. A method asin claim 2 wherein :said metallayers comprise overlapping ends of a single metal layer.

13. A method as in. claim 3 wherein at least oneof said metal layers comprisesua plurality of single layers bonded 1 together.

14. A method of claim .Zwherein said angle is about from 1 to.32' and said ductile-metal layers are selected from-the group consisting of :iron, titanium, niobium, tantalum, silver, nickel, magnesium, copper, zirconium and their alloys.

15-. A processof claim 14 whereinsaid twolayersare of titanium and steel respectively.

References I Cited by the Examiner UNITED STATES PATENTS 3,137,937 6/1964 Cowan et al.; 2 9,487 X JOHN F. CAMPBELL, Primary Examiner. 

1. A METHOD FOR FORMING A SUBSTANTIALLY CONTINUOUS METALLURGICAL BOND BETWEEN METAL LAYERS WHICH COMPRISES FORMING A JUNCTURE BETWEEN AT LEAST TWO DUCTILE METAL LAYERS, SAID JUNCTURE BEING DEFINED BY AN ANGLE OF ABOUT 1 TO 60*, POSITIONING A LAYER OF A DETONATING EXPLOSIVE ON THE EXTERNAL SURFACE OF AT LEAST ONE OF THE METAL LAYERS, AND INITIATING THE EXPLOSIVE SO THAT AT LEAST ONE OF THE RATIOS OF THE COLLISION VELOCITIES TO THE RESPECTIVE SONIC VELOCITIES OF THE METAL LAYERS IS LESS THAN 1.2 AND WHEN EACH OF THESE RATIOS IS GREATER THAN 1.0 THE ANGLE BETWEEN EACH TWO ADJACENT METAL LAYERS IN THE COLLISION REGION EXCEEDS THE MAXIMUM VALUE OF THE SUM OF THE DEFLECTIONS PRODUCED IN THE METAL LAYERS BY OBLIQUE SHOCK WAVES, THE LOADING OF SAID EXPLOSIVE BEING AT LEAST THAT WHICH PRODUCES A COLLISON PRESSURE GREATER THAN 100% OF THE ELASTIC LIMIT OF THE METAL HAVING THE LOWEST ELASTIC LIMIT IN THE SYSTEM. 